This invention relates to an aluminum electrolytic capacitor containing as electrolyte 79-95 wt. % of an azeotrope of acetic or propionic acid and triethylamine or tri-n-propylamine, 5-20 wt. % water, and up to 1 wt. % phosphoric acid. The electrolyte has a low enough resistivity to make it suitable for low-voltage capacitors.
Azeotrope electrolytes used in 25-60 V electrolytic capacitors have low volatility, good low temperature properties, and good shelf life. The azeotropes have been used with and without other solutes or other solvents. Generally, these electrolytes have not contained any additional water other than that introduced inadvertently.
There is a current demand for 10 V or lower capacitors. The electrolytes for these capacitors should have a resistivity below 200 .OMEGA.-cm and preferably less than 150 .OMEGA.-cm. It had been shown that conductive solutes, e.g., nitrates, lowered resistivity; however, nitrates are not compatible with aluminum foil so highly conductive organic solutes were added to the azeotropes. The results were highly disappointing, and in one case a violent reaction occurred. It had also been shown that the azeotropes could be used with capacitor solvents. When the azeotropes were mixed with low resistivity, polar solvents, the results were again disappointing.